“Did you get your flu shot?” If your friends are anything like mine, you heard this question at least a dozen times before Thanksgiving. You probably got your fair share of disdainful looks too, if you answered “No.” But why are we worried about getting the flu shot now and not in May? Why is there a flu season at all? After all, what does a virus living in a host who provides a dependable, cozy incubation chamber of 98°F, care whether it is freezing and snowy outside or warm and sunny? This question has bothered people for a long time, but only recently have we begun to understand the answer.
What is the Flu?
In order to discuss why we have a flu season, we must first understand what the flu is. The flu, also called influenza, is a viral respiratory illness. A virus is a microscopic infectious agent that invades the cells of your body and makes you sick. The flu is often confused with another virus, the common cold, because of the similarity in symptoms, which can include a cough, sore throat, and stuffy nose. However, flu symptoms also include fever, cold sweats, aches throughout the body, headache, exhaustion, and even some gastro-intestinal symptoms, such as vomiting and diarrhea (1).
The flu is highly contagious. Adults are able to spread the virus one day prior to the appearance of symptoms and up to seven days after symptoms begin. Influenza is typically spread via the coughs and sneezes of an infected person (1). Around 200,000 people in the United States are hospitalized each year because of the flu, and of these people, about 36,000 die. The flu is most serious for the elderly, the very young, or people who have a weakened immune system (1).
The Flu Season
The flu season in the U.S. can begin as early as October, but usually does not get into full swing until December. The season generally reaches its peak in February and ends in March (2). In the southern hemisphere, however, where winter comes during our summer months, the flu season falls between June and September. In other words, wherever there is winter, there is flu (3). In fact, even its name, “influenza” may be a reference to its original Italian name, influenza di freddo, meaning “influence of the cold” (4).
A common misconception is that the flu is caused by cold temperatures. However, the influenza virus is necessary to have the flu, so cold temperatures can only be a contributing factor. In fact, some people have argued that it is not cold temperatures that make the flu more common in the winter. Rather, they attest that the lack of sunlight or the different lifestyles people lead in winter months are the primary contributing factors. Here are the most popular theories about why the flu strikes in winter:
1) During the winter, people spend more time indoors with the windows sealed, so they are more likely to breathe the same air as someone who has the flu and thus contract the virus (3).
2) Days are shorter during the winter, and lack of sunlight leads to low levels of vitamin D and melatonin, both of which require sunlight for their generation. This compromises our immune systems, which in turn decreases ability to fight the virus (3).
3) The influenza virus may survive better in colder, drier climates, and therefore be able to infect more people (3).
The Flu Likes Cold, Dry Weather
For many years, it was impossible to test these hypotheses, since most lab animals do not catch the flu like humans do, and using humans as test subjects for this sort of thing is generally frowned upon. Around 2007, however, a researcher named Dr. Peter Palese found a peculiar comment in an old paper published after the 1918 flu pandemic: the author of the 1919 paper stated that upon the arrival of the flu virus to Camp Cody in New Mexico, the guinea pigs in the lab began to get sick and die (4). Palese tried infecting a few guinea pigs with influenza, and sure enough, the guinea pigs got sick. Importantly, not only did the guinea pigs exhibit flu symptoms when they were inoculated by Palese, but the virus was transmitted from one guinea pig to another (4).
Now that Palese had a model organism, he was able to begin experiments to get to the bottom of the flu season. He decided to first test whether or not the flu is transmitted better in a cold, dry climate than a warm, humid one. To test this, Palese infected batches of guinea pigs and placed them in cages adjacent to uninfected guinea pigs to allow the virus to spread from one cage to the other. The pairs of guinea pig cages were kept at varying temperatures (41°F, 68°F, and 86°F) and humidity (20%-80%). Palese found that the virus was transmitted better at low temperatures and low humidity than at high temperatures and high humidity (see Figure 1).
Figure 1 ~ Experimental Setup. Guinea pigs were housed in adjacent cages. Guinea pigs in cage 1 were infected by Palese with influenza. Palese observed how many guinea pigs in cage 2 became infected from the guinea pigs in cage 1 at different temperatures and levels of humidity. B, C) Transmission rates were 100% at low humidity, regardless of temperature. At high humidity, transmission occurred only at the lower temperature.
However, Palese’s initial experiment did not explain why the virus was transmitted best at cooler temperatures and low humidity. Palese tested the immune systems of the animals to find out if the immune system functions poorly at low temperatures and low humidity, but he found no difference in innate immunity among the guinea pigs (5). A paper from the 1960s may provide an alternate explanation. The study tested the survival time of different viruses (i.e. the amount of time the virus remains viable and capable of causing disease) at contrasting temperatures and levels of humidity. The results from the study suggest that influenza actually survives longer at low humidity and low temperatures. At 43°F with very low humidity, most of the virus was able to survive more than 23 hours, whereas at high humidity and a temperature of 90°F, survival was diminished at even one hour into incubation (3).
The data from these studies are supported by a third study that reports higher numbers of flu infections the month after a very dry period (6). In case you’re wondering, this is only the case in places that experience winter. In warmer climates, oddly enough, flu infection rates are correlated most closely with high humidity and lots of rain (6). Unfortunately, not much research has been done to explain these contradictory results, so it’s unclear why the flu behaves so differently in disparate environments. This emphasizes the need for continued influenza research. Therefore, we can conclude that, at least in regions that have a winter season, the influenza virus survives longer in cold, dry air, so it has a greater chance of infecting another person.
Although other factors probably contribute as well, the main reason we have a flu season may simply be that the influenza virus is happier in cold, dry weather and thus better able to invade our bodies. So, as the temperature and humidity keep dropping, your best bet for warding off this nasty bug is to get your flu shot ASAP, stay warm, and invest in a humidifier.
Hannah Foster is a PhD candidate in the Molecules, Cells, and Organisms program at Harvard University.
For more information about the flu, check out this video:
References
1) Medical News Today. What is flu? What is influenza? What are the symptoms of flu? < >[2 November, 2014]
2) Centers for Disease Control. The Flu Season. <http://www.cdc.gov/flu/about/season/flu-season.htm> [2 November, 2014]
3) Elert, E. 2013. FYI: Why is There a Winter Flu Season? Popular Science. <http://www.popsci.com/science/article/2013-01/fyi-why-winter-flu-season> [2 November, 2014]
4) Kolata, G. 2007. Study Shows Why the Flu Likes Winter. New York Times. <http://www.nytimes.com/2007/12/05/health/research/05flu.html?_r=1&> [2 November, 2014]
5) Lowen, A.C., S. Mubareka, J. Steel, and P. Palese. 2007. Influenza Virus Transmission Is Dependent on Relative Humidity and Temperature. PLOS Pathogens. 3(10):e151.
6) Roos, R. 2013. Study: Flu likes weather cold and dry or humid and rainy. University of Minnesota Center for Infectious Disease Research and Policy. <http://www.cidrap.umn.edu/news-perspective/2013/03/study-flu-likes-weather-cold-and-dry-or-humid-and-rainy> [14 November, 2014]
I’ve never had flu, touch wood.. But every time I get a cold, I immediately know as I feel a certain tickle sensation in one of my nostrils that is different to anything else. I know instantly when a cold has ‘landed.’ However, If I’m lucky enough to have tiger balm on me, (which I use for headaches) and I place the tiger balm on the spot inside the nostril, the cold never lasts more than one day. If I don’t do this, (no tiger balm available at the right moment) I’m in for the long haul.. Can you tell me why this might work. I’m not scientific in any way, lol..
I get the exact same “tickle” feeling! Oddly, it’s only been in the past few years I’ve noticed this. If you start taking vitamin C every two hours at the slightest hint (sneeze, throat scratchiness, the tickle in the nose etc) – 500-1000 mg for an adult , and/or drink an antiviral herb tea (1 tbsp per 1 cup using thyme, basil or oregano) 3-4 times a day, this can (and most often does, for me) push off whatever it is. I had to fight these viruses/colds/flu like 7-8 times this season. I have no idea why the season should be so drastically different than it has my entire life, but most seasons I might fight a cold/virus or flu ONCE the entire season. Unfortunately this last time I felt a slight sore throat and managed to fight it completely off of me…late in the 2nd successful day of having zero symptoms, I suddenly picked it up again prob from the air (my husband is sick as well). This time I’m managing to push it off but I ran out of vitamin C so it’s been a bit more stubborn . I honestly can’t help but think that our bodies are meant to have much higher levels of C regularly throughout the day than we normally get. I’m not sure about the tiger balm. I’m assuming it has oils in it ; do viruses need to “breathe”?
Placebo is the term for your experiences.
Patronising is the term for your reply.
Lol Jake……..
In our state (Queensland, Australia), the tropical part (Cairns, Townsville etc.) gets ‘flu at the time as the sub-tropics (Brisbane etc.) and plenty. There is certainly no shortage of ultraviolet light in Cairns in the Winter, and the temperature rarely falls below 20C, even at night (26-30 during the day). Seems to me there must be some other explanation than climate factors (temperature or humidity). It astounds me that we still haven’t figured this out!
From the figures, it looks like the humidity decides the transmission of the virus. Brisbane in my impression is not so humid enough, although not cold. In most area, the hotter, the more humid, but not the case for Brisbane.
Does this information apply to the Common Cold the same as it does the Flu?
This research was only done on the flu virus, so cold viruses might thrive in different conditions.
i would like to address your hypothesis that the reduced hours of sunlight during the winter negatively affect people and could contribute to flu transmission.
While there *are* fewer hours of sunlight during the winter, other factors also affect the manufacture of vitamin D and melatonin. First of all, during winter, the sunlight strikes higher latitudes at a much greater angle of incidence. Imagine that you are standing on the equator at noon on the spring or fall equinox. Imagine that the sunlight falling on you is a long tube of one foot radius connecting you to the surface of the Sun. The sunlight comes straight down, and hits the ground and shines on an area of pi square feet. The energy is very concentrated.
But imagine instead that you are standing in Chicago, at 43ºN latitude on the winter solstice, when the Sun is directly overhead at a point 22.3ºS latitude. The sunlight falls on you at 64º off from straight overhead. The formula for the area of an ellipse formed by cutting a cylinder of radius r at angle α is A = pi * r^2/ sin(α). For a cylinder of 1 foot and an angle of 64º, this gives us an area of 1.11 square feet, for an 11% increase in area or a 12% decrease in energy because it is spread over that increased area.
All of this assumes that you are spending just as much time outside, which of course is generally not true. In the summer your typical cubicle worker is eager to spend the weekend outside if the weather is nice. In the winter, even if it is sunny, the average person won’t spend all day at the beach when it’s 10ºF. Plus, in the winter, even if you are outside, you are bundled up. At 10ºF, a person outside will wear clothing over all of their body except maybe their face. This is entirely different from the clothing worn when it’s 80ºf outside, in which 50-90% of the body is uncovered.
In short, it is not just the hours of sunlight available that are reduced in the winter.
In winter we wear a lot more clothing and absorb far less sun light on our person. I think the changes in clothing may have a larger affect than the reduced hours of sunlight.
Are colds and the flu as common in San Francisco, CA (relatively milder climate most of the year) as in New York City (relatively much colder in the winter months, but somewhat warm/hot and humid in summer compared to San Francisco)? Thank you very much.
Please do explain whether in warmer cities in the USA – for example, Los Angeles, San Diego – people suffer fewer colds than, say, in New York City, Boston, etc. during the winter months. And, are there any places in the world where people almost never catch colds and/or the flu? What about parts of the world where the flu is much more common than the rest of the world? Thank you very much.
You might want to take a look at this interactive map from the CDC. You can review the levels of reported flu cases regionally over several seasons. https://gis.cdc.gov/grasp/fluview/main.html
A quick review suggested to me that all of California is generally at a lower incidence level than the rest of the US.
I think the flu/colds are spread more easily where there are lots of people in closed, confined spaces (major metropolitan areas) because it can more easily spread from one person to another! Plus, people’s immune systems differ depending maybe on genetics!
because that is the capitol of satan. why would he want to spread disease where all his core employees rest?
California visuses are more laid back.
I know this is long past when you sent it, but it makes sense when southern Californians can be outside more with more open air. Thank you for sounding intelligent and guiding people towards facts!
The common cold is a man-made virus which is released every year into the populous around Autumn time in various heavily populated major towns around the world. The untold truth is that this is a way of governments to control the ever aging and growing population of the world. I have personal evidence of dealing with the secret organisation that is responsible for population control. The proof is out their in-front of everyone’s eyes in black and white, I mean come on how is it that everyone seems to get the flu or colds in winter???? think about it! there’s more chance you’ll kick the bucket due to colder weather, therefore yielding a higher mortality success rate. Its a cruel world but the truth needs to be told!
How did people get colds before we had the technology to manipulate DNA? How did people get colds in the 1800s? In the 1700s?
In the 1500’s the spanish conquistadors brought the virus that causes smallpox to the Aztecs and wiped them out.
From PBS:
The ability of smallpox to incapacitate and decimate populations made it an attractive agent for biological warfare. In the 18th century, the British tried to infect Native American populations. One commander wrote, “We gave them two blankets and a handkerchief out of the smallpox hospital. I hope it will have the desired effect.”
Not only did they try, but unfortunately they were successful.
The same way they get colds now: by infections from others who have it. Basic immunology.
OMG! Are you serious?
Lord Jeffrey Amherst and Lord Cornwallis both used the infected blanket method.
Might want to loosen that foil hat buddy
@Simon
You must be 12 years old. How cute.
I heard that the government made sharks 2. They release them all year to keep us out of the oceans!
Wake up people!!
Id like to see the proof of this. I’m not saying that you are wrong about that. Our government misleads us all the time. I bet you are a believer in aliens also. I know I am a believer. I’ve seen them.
So when your mother would say, “put on a winter coat you might catch a cold” she had the wrong assumption? At least you didn’t get hypothermia.
On a side note I remember watching a story on tv of a man who lived isolated in the woods of Maine in a homemade tent for many years and after being found he reported never getting sick even throughout the brutal winters. It might help prove that it’s not the cold temp that gets you sick, but just contact with people who spread the virus.
However when the majority of people are in close contact this is interesting to consider that the virus spreads more easily in colder drier air! Some comments disagree with this because in Florida they apparently have a bad flu season. However don’t forget that FL is probably still the number one vacation destination in the world (Disney) and when do many people travel there – from the north during flu season!
In that scenario, the more logical assumption is that it has a lot to do with not being in contact with other people. It’s mainly an airborne transmitted infection spread via droplets from cough, sneeze, etc. But even if infected from physical contact, the virus can only survive so long on surfaces outside the body. So if you’re isolated during flu season, I can’t imagine how you’d catch it.
Your mother was right. Just because a virus is present doesn’t mean you’ll catch it. Protecting yourself from cold means the virus doesn’t have ready-made access to your system. The warmer you are, the less able a virus will enter your body.
I assure you the Flu thoroughly enjoys playing in your nice warm 98.6F body. Give it a pathway and it will happily slip in there and have a party. And it doesn’t really matter what the season is either. If you come in contact with just ONE viable specimen that came from God knows where, then you get infected. That’s how people get the Flu in the Hot Humid Summer. It hitches a ride with a carrier and you pick it up because you thought you were safe in the Summer. Sorry, but the Flu is active all year long. There’s just a higher risk of transmission when more people are gathered together under lower humidity conditions, that’s all.
@TimS is the assumption that because no true absolute recovery occurs for all flu infected persons there is a perpetual spread of flu? I read this article because it seemed to me that essentially there should be a time that the flu is nonexistent. There should be a day where everyone in any given year has either had, been immune to, or not had the flu. On that day, the flu should cease to exist. The most insightful information in the article for me was not fully explored. That global travel does not allow there to be a day like that because some group of people in the opposite hemisphere are experiencing a flu outbreak and they spread it. It certainly seems obvious to me based on this article and the relatively short period for viral viability that if we restricted travel for people experiencing flu or its symptoms for the viability it would die out. No one can say its too hard to do now. Goverments had gone to extremes to keep people isolated to prevent the spread of COVID-19. For instance, if this research is true and population is not being manipulated then there should not be any more flu. It should literally die out. If a person is sick with flu (somehow) at the end of this global quarantine period, then they should be treated with the same care (level of PPE for hazmat) as COVID-19. That would significantly reduce the spread of that person’s viral load. Someone tell me why I’m wrong. PLEASE.
So, you’re saying that when I got the Flu in 2016 that all my family that I came in contact with (which was at least: two 65+ year olds, my 60 year old mother who was dying of cancer, a 30 year old, a 2 year old and a 6 month old baby–both of whom had only mother’s immunity to protect them since they never went to daycare or got vaxxed) contracted the virus? Yet none of those aforementioned people got sick at all. I have never in my life had a flu shot and the last time i had flu before 2016 was so long ago i cannot tell you–probably 15 or more years. Yeah….I’m gonna call BS on your “theory.” sorry. I don’t think Every One i came in contact with contracted the flu. Where does this magical flu spring out from every “flu season” anyway? hmmm. interesting. Even the article is clear that the tests were contradictory and therefore inconclusive, needing further research. Yet Timmy here has all the answers. LOL.
Regarding Florida virus deaths in warm, moist weather. It’s partly the migrations from the north to Disney. But also consider the much older population of older retirees. Many have less effective or compromised immune systems.
..
To @tims. There doesn’t seem to be a time when everybody has been exposed to the flu. Thus there is year round infection. it is just significantly more quiescence in warm weather with less spreading. There is also viral genetic change constantly occurring so that even though you got the flu this year, you may get it next year as your immune system may not recognize it.
> a man who lived isolated in the woods of Maine in a homemade tent for many years and after being found he reported never getting sick even throughout the brutal winters. It might help prove that it’s not the cold temp that gets you sick, but just contact with people who spread the virus.
No it doesn’t prove anything. We already know that viruses exist and they spread by contacts, so it’s not surprising the man never got sick. But it doesn’t mean that cold doesn’t make it easier for them to spread.
You are aware that its called germ “theory” for a reason right? its not a proven fact, its a theory. You don’t know anything. You are probably not a virologist, immunologist or even a doctor for that matter. Not all doctors agree on theories. Almost every single major breakthrough in Medicine or Science has not come from the people who thought exactly like everyone else and followed the herd. It came from those who defied long-held beliefs and dared to oppose popular opinion. Most were thought of as crazy. Yet here we are….. I’m so glad people could think for themselves once upon a time.
Are you saying that you don’t believe germ theory is true ?
their, there and they’re… no one is going to listen to your theories until you get that worked out.
Intelligence isn’t the same as grammar proficiency. I’m a professional writer, and I make mistakes. Intellectual snobbery has held society back from a lot of great discoveries and advancements. If your mind is not open to learning because of your inability to see past grammatical errors, then isn’t your intellect the problem (and anyone who has the same issue)?
Thank you for saying this!
if they wanted to kill off people… wouldn’t it be much easier to just shut the electricity off?
are you the real simple simon
Would they not then be infecting their own friends and family and themselves too ?
I have wondered if UVB tends to destroy cold and flu viruses. Near sea level UVB becomes significant when the sun is more than about 45 degrees above the horizon.
What is your evidence??
The coment bellow totally killed yours. In the past do you also believe the spanish government created influenza?
First sentence. You’re incorrect. Virus starts with and emanates (comes) from) other than humans. Usually, animals or mutations of other less harmful viruses
Populace. The rest of your belief is typical modern day paranoia with no basis in facts. For example, this secret organization for population control must have a reduced number in mind. So, why is the world population still increasing despite many, many decades of flu of all types? Are they based in Area 51 or Atlantis? Autumn time = autumn. Way for, not of. Their s/b there. Oh, the flu grows far better in cold, dry weather. That’s why your secret organization releases it in the winter. Relax. Read some actual science while drinking down a zinc pill with some orange juice.
https://ourworldindata.org/grapher/number-of-deaths-per-year
Explain the UN projection for the rest of the century
I agree, I knew this back in the 1950’s most people knew it. Anyway , you can kill this virus with heat. watch youtube.( Conquering Covid-19) Also be taking vitamin C and Zinc. Eat good, lots of veggies, fruit. no sugar or flour. Keep immune system up. Follow all the other things, washing hands etc.
My grandmother who was part native American would wrap us in a wool blanket after giving us a hot toddy and mineral oil when we got the flu or pneumonia. We would be over it in a day or two. Disease starts in the gut. Keep those intestines in good shape.
Native Americans died just like all the rest of us, only usually at a younger age. There was nothing “magic” in their cures or preventative measures. Some survived for a whIle but all ultimately died. Just like anyone else.
We’re all thinking about it in 2020
Why don’t you unleash this evidence and share your information? why would you not share this so-called evidence?
I think that in Russia (looking and watching what is gaoing on, mosto people are ill, doctors can’t say that the desease is what) the virus is spread by our Government to male the sales of drugstores. I think that it is the imune system that is working. I don’t get used to the tablets and was cured by berries and the same in the childhood. I was surrounded by virused people including my mom but there’s no virus in me.
Please read my comments as you are on the right path!
Please rewrite this.
thank you for interesting article. Please can you be more specific, in the graphics (and text) you do not specify if it is relative or absolute humidity. However, since expressed in % one may assume it is relative humidity. On the basis that the absolute humidity is important to organism, then lower temperature means lower absolute humidity at given relative humidity. Otherwise put, lower temperatures are MUCH drier than warm at same relative humidity. The temperature being colder accentuates the humidity effect. Thank you for contact by email with any useful publications.
regards, n
Thanks for your question! The original paper is cited in the references, and says that it is relative humidity : http://journals.plos.org/plospathogens/article?id=10.1371/journal.ppat.0030151
No mention of any research of mosquitos spreading the flu for thousands of years…not even a comment on it. Interesting considering they have been spreading many virus for ever.
Influenza is not a blood-borne virus. Therefore it cannot be transmitted by mosquitoes.
I think we would have seen a huge hike in Coronavirus during the mosquito period – which I was wondering about too, as it is in effect injected into the bloodstream through the means by which the insect obtains its meal – but any transmission of disease by mosquitoes, may depend upon the frequency of their feeding, or the insect’s own cleaning routine/immune system. Lots of lovely variables to consider.
That isn’t how the flu is spread though. Mosquitos transmit other viruses like Malaria for ex or Yellow fever. Now, secondly if the flu is most active in winter, there are no mosquitoes in winter in cold climates. Mosquitos which thrive in tropical or warm climates seem to transmit viruses which thrive in warm climates such as the ones I mentioned and the flu does not thrive in warm climates. But third and most importantly is for a disease to transfer to another species it has to first be able to infect and effect the first species.
The “Sweet Spot” of temperature and humidity favoring the influenza virus is cold enough to preserve its surface and spike proteins and persistence of mist. Hydrophilic amino acid sequences denature more rapidly at elevated temperature and aerosol droplets evaporate more quickly at dry relative humidity. A few point close to a cool temperature favors the longevity of the virus and the vehicle of the most the transmits the contagion. Low temperature with a slightly lower dew point (by one to ten degrees Celsius) creates a high relative humidity and temperature stabilized virus to exponentially increase the probability of influenza transmission and infection.
Spell correction is a problem. – Change “Few” to “Dew” in moisture references of DEW POINT”, the is the temperature at which water at a vapor pressure will condense as water or ice.
And in line 3 change “vehicle of the most the transmits” to “vehicle of the mist that transmits”?
Perfect answer. And why ‘Joggers’ breath’ is probably more dangerous at lower temperatures in regard to spreading coronavirus, as it persists – often visibly – as an aerosol after the jogger has ‘jogged on’! I can’t find any papers on RH in classrooms, offices, public transport – can you suggest? – but I came looking for Winter vs Summer conditions and their effect on the seasonal level of common cold infections, also a coronavirus, therefore likely to indicate useful routes to infection.
Reading this article has provided me with some much need insight that I can share with patients, co-workers, family and friends. Thanks so much!
This fake cuz the way it was written so fake fake fake fake fake fake fake
You’re fake because of the way you talk
Who read it to you?
Sup…How is the way it was writen, make it fake? Your speech isn’t exactly intellegent! How about facts, not assumption?
I bet be can at least spell ‘intelligent’!
Much like this comment.
You watch too much “fake” news.
Everything reported on the news is fake asf !
Good point. Relative humidity is not a terribly useful measure for any purpose.
Relative Humidity is an important measure when determining if contrails will form and persist.
Of if fog will form soon.
What nonsense. Flu likes warm moist environments. Therefore when it is called it finds a host to survive. If the air is warm and moist it has no need to find a host. That is why infections increase in winter. Therefore Flu dislikes cold and dry climate.